Flask-APScheduler 作业中的查询模型引发应用程序上下文 RuntimeError

Question

我想使用 Flask-APScheduler 运行一个查询 Flask-SQLAlchemy 模型的作业。当作业运行时，我得到

RuntimeError: application not registered on db instance and no application bound to current context

。如何运行查询数据库的作业。

from flask_apscheduler import APScheduler

scheduler = APScheduler()
scheduler.init_app(app)
scheduler.start()

from models import User

def my_job():
    user = User.query.first()
    print(user)

查询时出现错误，还没来得及打印。该数据库在应用程序的其余部分中用于其他查询。

我在设置扩展程序时尝试添加

with app.app_context():

，但这没有用。

with app.app_context()
    scheduler = APScheduler()
    scheduler.init_app(app)
    scheduler.start()

完整的追溯是：

ERROR:apscheduler.executors.default:Job "run_in (trigger: interval[0:00:10], next run at: 2016-10-18 23:00:53 CEST)" raised an exception
Traceback (most recent call last):
  File "/Users/user/.virtualenvs/myfolder/lib/python2.7/site-packages/apscheduler/executors/base.py", line 125, in run_job
    retval = job.func(*job.args, **job.kwargs)
  File "/Users/user/Documents/myfolder/myfolder/myfile.py", line 19, in myjob
    user = User.query.all()
  File "/Users/user/.virtualenvs/myfolder/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 454, in __get__
    return type.query_class(mapper, session=self.sa.session())
  File "/Users/user/.virtualenvs/myfolder/lib/python2.7/site-packages/sqlalchemy/orm/scoping.py", line 71, in __call__
    return self.registry()
  File "/Users/user/.virtualenvs/myfolder/lib/python2.7/site-packages/sqlalchemy/util/_collections.py", line 878, in __call__
    return self.registry.setdefault(key, self.createfunc())
  File "/Users/user/.virtualenvs/myfolder/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 704, in create_session
    return SignallingSession(self, **options)
  File "/Users/user/.virtualenvs/myfolder/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 149, in __init__
    self.app = db.get_app()
  File "/Users/user/.virtualenvs/myfolder/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 845, in get_app
    raise RuntimeError('application not registered on db '
RuntimeError: application not registered on db instance and no application bound to current context

Answer 1

Flask-SQLAlchemy 需要一个活动的应用上下文来执行查询。虽然 Flask-APScheduler 确实将 APScheduler 与 Flask 集成，但它不会在运行每个作业时推送应用程序上下文。

你需要在你的工作中推送应用上下文。设置扩展程序时推送应用程序上下文不会执行任何操作。

def my_job():
    with app.app_context():
        ...

您可能需要所有作业的应用程序上下文。您可以子类化扩展并覆盖

run_job

.

from flask_apscheduler import APScheduler as _BaseAPScheduler

class APScheduler(_BaseAPScheduler):
    def run_job(self, id, jobstore=None):
        with self.app.app_context():
            super().run_job(id=id, jobstore=jobstore)
            # super(APScheduler, self) in Python 2

Answer 2

我通过强制 Flask-SQLAlchemy 扩展在应用程序工厂内处于单应用程序模式来解决这个问题。这在技术上是不正确的，可能会在其他地方引起问题，但它解决了我的具体问题。

def create_app():
    new_app = Flask(__name__)
    db.init_app(new_app)
    db.app = new_app
    return new_app